How do I add image dividers around my banner?

heres the code

/* Banner */

main:before {

width: auto;

height: 200px;

display: block;

content: "";

background-image: url(my image thang);

background-position: center center;

background-size: cover;

margin-bottom: 25px;

margin-top: 15px;

background-size: 84%;

}